Regulation of Nitrate Reductase Activity in Corn (Zea mays L.) Seedlings by Endogenous Metabolites

Application and effectiveness of Methylobacterium symbioticum as a biological inoculant in maize and strawberry crops

The effectiveness of Methylobacterium symbioticum in maize and strawberry plants was measured under different doses of nitrogen fertilisation. The biostimulant effect of the bacteria was observed in maize and strawberry plants treated with the biological inoculant under different doses of nitrogen fertiliser compared to untreated plants (control). It was found that bacteria allowed a 50 and 25% decrease in the amount of nitrogen applied in maize and strawberry crops, respectively, and the photosynthetic capacity increased compared with the control plant under all nutritional conditions. A decrease in nitrate reductase activity in inoculated maize plants indicated that the bacteria affects the metabolism of the plant. In addition, inoculated strawberry plants grown with a 25% reduction in nitrogen had a higher concentration of nitrogen in leaves than control plants under optimal nutritional conditions. Again, this indicates that Methylobacterium symbioticum provide an additional supply of nitrogen.

Methylobacterium symbioticum sp. nov., a new species isolated from spores of Glomus iranicum var. tenuihypharum

Strain SB0023/3 ^T, isolated from spores of the arbuscular mycorrhizal fungus Glomus iranicum var. tenuihypharum, was analysed to determine whether it represents a new species. It was studied for its applicability in the field of agriculture to reduce the input of nitrogen fertilizers. Comparative analysis of the 16S rRNA gene sequence shows the strain to be affiliated to the genus Methylobacterium, the closest similarities (98.7%) being shared with Methylobacterium dankookense. Further phylogenomic analysis through Up-to-date Bacterial Core Gene (UBCG) confirmed Methylobacterium dankookense as its closest relative. Average Nucleotide Identity (ANI) and in silico DNA-DNA hybridization (DDH) were lower than 92% and 44%, respectively, of the values shown by its phylogenetic relatives. Its genome had an approximate length of 6.05 Mb and the G + C content of the genome was 70.1 mol%. The main cellular fatty acid was Summed Feature 8 (C_18:1ω7c and/or C_18:1ω6c). It is a Gram-staining-negative, pink-pigmented, strictly aerobic and facultative methylotroph; it grows at 28 ºC and can grow at up to 3% salinity in the presence of sodium chloride. All the data collected support the naming of a novel species to accommodate the strain SB0023/3 ^T, for which the name Methylobacterium symbioticum sp. nov. is proposed. The type strain is SB0023/3 ^T (=CECT 9862 ^T =PYCC 8351 ^T).

Ammonium and amino acids as regulators of nitrate reductase in corn roots

When amino acids or ammonia are added to plant systems, the effects on the development of nitrate-dependent nitrate reductase activity are variable. In addition, amino acids added singly or as casein hydrolysate may not support a normal growth. A physiologically correct mixture of amino acids, one similar in composition to amino acids released by the endosperm, has been shown to support normal growth and protein synthesis in corn (Zea mays) embryos. In this investigation, we have used the mixture of corn amino acids to determine whether amino acids have an effect on the appearance or disappearance of nitrate reductase activity. The results show that these amino acids partially inhibit the induction of nitrate reductase in corn roots. The effect is more pronounced in mature root than in root tip sections. When glutamine and asparagine are included along with the "corn amino acid mixture," the inhibition is more severe. Amino acids or amino acid analogues added singly to the induction medium have a similar effect: i.e. when the induction of nitrate reductase is inhibited in the root tips (lysine, canavanine, azaserine, azetidine-2-carboxylic acid, dl-4-azaleucine, asparagine, and glutamine), that inhibition is more severe in mature root sections. Arginine enhanced the recovery of nitrate reductase in root tips but inhibited it in mature root sections. The effect of the amino acids is apparently on some phase of the induction processes (i.e. the uptake or distribution of nitrate or a direct effect on the synthesis of the enzyme) and not on the turnover of the enzyme.

Differential regulation of nitrate reductase induction in roots and shoots of cotton plants

The induction of nitrate reductase activity in root tips of cotton (Gossypium hirsutum L.) was regulated by several amino acids and by ammonium. Glycine, glutamine, and asparagine strongly inhibited induction of activity by nitrate and also decreased growth of sterile-cultured roots on a nitrate medium. Methionine, serine, and alanine weakly inhibited induction, and 11 other amino acids had little or no effect. Ammonium also decreased induction in root tips, but was most effective only at pH 7 or higher. The optimum conditions for ammonium regulation of induction were identical to those for growth of sterile-cultured roots on ammonium as the sole nitrogen source. Aspartate and glutamate strongly stimulated induction, but several lines of evidence indicated that the mechanism of this response was different from that elicited by the other amino acids. The effects of amino acids on induction appeared to be independent of nitrate uptake.In green shoot tissues, all attempts to demonstrate regulation of induction by amino acids failed. The great difference in observed responses of root and shoot to amino acids suggests that their nitrate reductase activities are regulated differently. Differential regulation of this enzyme is consistent with the responses of root and shoot nitrate reductase activity to nitrate.

Regulation of nitrate reductase in Neurospora crassa: stability in vivo

Nicotinamide adenine dinucleotide phosphate, reduced form (NADPH)-nitrate reductase and its related enzyme activities, NADPH-cytochrome c reductase and reduced benzyl viologen-nitrate reductase, are all induced following the transfer of ammonia-grown wild-type Neurospora mycelia to nitrate medium. After nitrate reductase is induced to the maximal level, the addition of an ammonium salt to, or the removal of nitrate from, the cultures results in a rapid inactivation of nitrate reductase and its two partial component activities. This rapid inactivation is slowed down by the protein synthesis inhibitor, cycloheximide. Experiments on the mixing of extracts in vitro rule out the presence of an inhibitor of nitrate reductase in free form in extracts containing inactivated nitrate reductase. Ammonia does not inhibit the uptake of nitrate by the mycelia. Inactivation of nitrate reductase in vivo by ammonia depends on the concentration of the ammonium salt and is not reversed by increasing the nitrate concentration of the medium. The nitrate-inducible NADPH-cytochrome c reductase activity and reduced benzyl viologen-nitrate reductase activity respectively of the nitrate-nonutilizing mutants nit-1 and nit-3 are not inactivated in vivo by the addition of an ammonium salt or the withdrawal of nitrate. This finding suggests that the integrity of the nitrate reductase complex is required for the in vivo inactivation of nitrate reductase and its associated activities.

Regulation of nitrate reductase in excised barley roots

When excised barley roots (Hordeum distichum L.) are appropriately pretreated, the level of nitrate reductase in the roots increases upon exposure to nitrate. Relatively low levels of nitrate (10 mum) gave maximum induction of nitrate reductase. This increase was inhibited by inhibitors of protein and RNA synthesis, indicating that de novo protein synthesis is probably involved. Induction of nitrate reductase by nitrate is partially prevented by the inclusion of ammonium, an eventual product of nitrate reduction, in the incubation medium. Under the experimental conditions used, ammonium did not inhibit the uptake of nitrate by excised barley roots. It is concluded, therefore, that ammonium, or a product of ammonium metabolism, has a direct effect on the synthesis of nitrate reductase in this tissue.

Nitrogen metabolism of Spirodela oligorrhiza : III. Amino acids and the utilization of nitrate

Wheras ammonium inhibited almost completely utilization of nitrate (NO3) by Spirodela oligorrhiza, asparagine, aspartate, glutamine, and glutamate had only a sparing effect. Asparagine and glutamine were used more rapidly than NO3; aspartate and glutamate at about the same rate. These differences in utilization of NO3 were not determined by differences in the levels of nitrate reductase.

Influence of nickel on the detection of nitrate reductase activity in sorghum extracts

The addition of nickel (4 x 10(-3)m) to the extracting buffer enhances the nitrate reductase activity in preparations of young grain sorghum (Sorghum bicolor L. [Moench] leaf tissue by as much as 6-fold. Activities comparable to other plant species are obtained over an extraction pH range of 7 to 8 with tris buffer and reduced nicotinamide adenine dinucleotide as a cofactor for the reaction when the ratio of plant material to extraction medium is 1:20. The method also enhances nitrate reductase activity in sudangrass (Sorghum sudanense P. [Stapf]).

The nitrogen metabolism of Spirodela oligorrhiza : II. Control of the enzymes of nitrate assimilation

Nitrate reductase (NO3R) in Spirodela oligorrhiza has a specific requirement for NAD, and no activity could be detected when reduced NADP was supplied as a cofactor. NO3R and nitrite reductase (NO2R) are adaptive enzymes, being present only when the plant is supplied with NO3 or NO2. There is significant correlation between the concentration of NO3 in plants, and the levels of NO3R that they contain. When plants not containing NO3R or NO2R are supplied with NO3, there was a rapid increase in the levels of the two enzymes and in the concentration of NO3 in the plants. These increases were retarded but not prevented by NH4 in the medium. When NO3-grown plants were depleted of N, there was a rapid decrease in the levels of NO3R and NO2R.The utilization of NH4 prevented the assimilation of NO3 even by plants that contained high levels of NO3R and NO2R. It was therefore concluded that NH4, or the processes or products of its assimilation must inhibit the activity of NO3R. NH4, arginine, asparagine or glutamine, tested separately or together, had little effect on the in vitro activity of NO3R.

Nitrogen metabolis of Lemna minor. II. Enzymes of nitrate assimilation and some aspects of their regulation

In L. minor grown in sterile culture, the primary enzymes of nitrate assimilation, nitrate reductase (NR), nitrite reductase (NiR) and glutamate dehydrogenase (GDH) change in response to nitrogen source. NR and NiR levels are low when grown on amino acids (hydrolyzed casein) or ammonia; both enzymes are rapidly induced on addition of nitrate, while addition of nitrite induces NiR only. Ammonia represses the nitrate induced synthesis of both NR and NiR.NADH dependent GDH activity is low when grown on amino acids and high when grown on nitrate or ammonia, but the activities of NADPH dependent GDH and Alanine dehydro-genase (AIDH) are much less affected by nitrogen source. NADH-GDH and AIDH are induced by ammonia, and it is suggested that these enzymes are involved in primary nitrogen assimilation.

The occurrence of nitrate reductase in apple leaves

Nitrate reductase utilizing NADH or reduced flavin mononucleotide (FMNH(2)) as electron donor was extracted from the leaves, stems and petioles, and roots of apple seedlings. Successful extraction was made possible by the use of insoluble polyvinylpyrrolidone (Polyclar AT) which forms insoluble complexes with polyphenols and tannins. The level of nitrate reductase per gram fresh weight was highest in the leaf tissue although the nitrate content of the roots was much higher than that of the leaves. Nitrite reductase activity was detected only in leaf extracts and was 4 times higher than nitrate reductase activity. Nitrate was found in all parts of young apple trees and trace amounts were also detected in mature leaves from mature trees. Nitrate reductase was induced in young leaves of apple seedlings and in mature leaves from 3 fruit-bearing varieties. An inhibitor of polyphenoloxidase, 2-mercaptobenzothiazole was used in both the inducing medium and the extracting medium in concentrations from 10(-3) to 10(-5)m with no effect upon nitrate reductase activity.

l-Phenylalanine Ammonia-Lyase Activity During Germination of Phaseolus vulgaris

l-Phenylalanine ammonia-lyase (PAL) activity develops in excised bean axes after approximately 5 hours of incubation and reaches a maximum level after 14 hours of incubation. Light does not affect the development of activity, but puromycin, cycloheximide, actinomycin D, and 5-fluorouracil inhibit.During this period of incubation both d- and l-p-fluorophenylalanine stimulate fresh weight increase and both inhibit the development of PAL activity. Neither l- nor d-phenylalanine stimulates fresh weight increase while the former inhibits development of PAL activity and the latter has no effect. Neither d isomer is deaminated while l-p-fluorophenylalanine is deaminated at about one-half the rate of l-phenylalanine. It is suggested that fluorophenylalanine does not stimulate the fresh weight increase by its effects on the phenolics pathway.Trans-cinnamic acid was found to inhibit both the development of PAL activity and the in vitro deamination of l-phenylalanine. Various hydroxycinnamic acids, although inhibiting the development of PAL activity, had little or no effect on the in vitro deamination of l-phenylalanine.No tyrosine ammonia-lyase activity was found in the axes and l-tyrosine had no effect on the in vitro deamination of l-phenylalanine.The pattern of PAL development in intact seedlings differs markedly from that which occurs in the excised axes, although light also has no effect on the course of activity.

Evidence for a role of calcium in nitrate assimilation in wheat seedlings

Severely Ca-deficient Triticum aestivum L. seedlings accumulated high levels of nitrite and moderate levels of nitrate and organic nitrogen, but contained unaltered levels of hydroxylamine. Nitrite accumulation was not related to molybdenum deficiency, or altered cellular pH. Nitrate reductase was decreased by Ca deficiency, apparently by repression of enzyme synthesis from accumulated nitrite and not by inhibition of enzyme activity. Nitrite reductase and NADP diaphorase activities were not affected by Ca deficiency, and Ca did not restore activity to nitrite reductase inactivated by cyanide. The results indicated that the role of Ca is in intracellular transport of nitrite and not in induction or activity of enzymes.